You are running across the street, late for an appointment, behind you there is a screeching noise. Your heart rate instantly zooms up to 180 BPM, the hair on your neck rises up, your capillaries contract while your veins dilate, your blood pressure goes up and you have an intense sensation of focus based on fear and adrenaline. You glance behind you and see two blocks away a sedan driving in the opposite direction. Whew!

What just happened there? Your brain and body acting on scant evidence prepared your organism to flee under threat of potential imminent disaster. Once removed, your heart rates start to calm down, your breathing slows, your eyes relax and other systems start to wash away the toxic byproducts of your fight or flight response. It might take a full half hour before you get back to some semblance of calm.

In the jungles and grassy plains of our evolutionary history being wary and prepared to jump at the first sign of trouble was a good thing. Our genes have triggers built into them, hard-wired for just this type of eventuality. Through long stretches of millenia, the ancestors who had a habit of scanning the horizon for hungry predators tended to live to procreate while those absent-minded apple munchers went the way of the dinosaurs.

Fast forward now to our present day and age. We no longer face the same pressures our ancient ancestors did, at least not in terms of immediate fight or flight from hungry predators. Current threats are much more abstract and couched in terms that our ancient ancestors would have been completely baffled by. Worried about your tax return? Wondering if Armageddon will show up on your door step any time soon?

It’s kind of unlikely your Roomba is planning to suddenly attack or your cat is going to go for your jugular. We live in relatively static environments of home and work where direct threats to our survival are very unlikely.

Human beings have wonderful cognitive systems dedicated to complex symbolic reasoning. When not focused on some direct cognitive task, our brains tend to revert to a state neurologists call the default network mode. It’s that mental place you get in where the task at hand is a bit boring or underwhelming and your mind wanders. It’s the day dreaming state.

In this default network mode, our evolutionary heritage tends to start looking for lions, tigers and bears, direct threats to our survival. Old memories of negative events may pop up. Foes or disasters, real or imagined. Our evolutionary brains are trying to help us out here by examining the data banks for potential threats even when there are none on the horizon.

Our brains don’t do a lot of sorting between the real and the imagined. Our bodies react similarly to a highly detailed imaginary threat as to a real one. Put this together with the default network mode of negative rumination and you have a brain whose default operating mode tends to get into negative ideation and depressing disaster contemplation.

If you combine rumination with a diet of constant media distraction, this can become a serious harm to your well being. News and events provided out of context, focused on disasters and other problems far removed from our own life can become a kind of backdrop of constant stress stimulation. It’s not that we shouldn’t be aware and educated about the state of the world, it’s the constant undertow of stress reactions to something occurring completely removed from our own circumstances that is problematic.

There are various antidotes to this problem. Since our bodies evolved in a highly vigorous and challenging physical environment, simply exercising regularly engages those physical systems that respond to stress in ways that directly relieves the problems that the stress response can cause. Exercise flushes away the toxic byproducts of stress so effectively that it is indeed a form of wonder drug, a free one that is built into your body’s pharmacology.

Having scripted internal monologues ready can also help when you notice your ruminations running into negativity. You can replace those thoughts with something simpler and more validating.

Over time, the best outcome is to replace negative ruminations with something better: an action, a thought, a behavior or a habit that is healthier and more life affirming than fear of lions and tigers and bears.